Capacitor potentiometer



Nov. 11, 1969 MIYAJI TOMOTA 3,478,256

CAPACITOR POTENTIOMETER Filed Oct. 18, 1967 .Iii. g. 1.

s FL OUT RF2 Y2 R Tn e I v TF2 v 5 I N VEN TOR.

By L @zQ, ATTORNEYS United States Patent US. Cl. 321--2 4 ClaimsABSTRACT OF THE DISCLOSURE A capacitor potentiometer having a transistorDC-AC converter for converting a DC-voltage into an AC signal having acertain amplitude, an impedance circuit including two variablecapacitors connected differentially with each other for changingmechanical motion into an electrical signal and a rectifier circuit forrectifying an output voltage of the impedance circuit.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a capacitor potentiometer employing variable capacitors forgenerating a standard voltage or to a non-contact type standard voltagegenerating apparatus which is suitable for use, for example, in theproduction of a balancing voltage for an automatic balancing-typerecording instrument and avoids defects experienced in the prior art.

Description of the prior art In conventional automatic balancing-typerecording instruments, the difference between an input DC voltage and astandard voltage is amplified by an amplifier; a balancing motor isdriven by an output signal of the amplifier to shift a slider of a sliderheostat to obtain a voltage balancing with the input signal; and thevalue of the input signal is known from the position of the slider.

However, the slide rheostat usually employed for producing the balancingvoltage in the conventional automatic balancing-type recordinginstruments presents problems in its reliability and durability as thecontacts of its slider are likely to be worn away and bad in contact.

SUMMARY OF THE INVENTION This invention is directed to a non-contacttype standard voltage generating apparatus which is free from thedrawbacks encountered in the prior art.

The primary object of this invention is to provide'a highly-precisioncapacitor potentiometer or a non-contact type standardvoltage-generating apparatus for producing a DC voltage in response toexternal displacements which comprises a constant-voltage AC oscillator,a voltage divider circuit including a differential capacity changerconnected to the output side of the oscillator and varying its capacityin response to external displacements, and a rectifier circuit forrectifying an output voltage of the voltage divider circuit to obtain aDC voltage, and which substantially eliminates the defects in the priorart.

Other objects, features and advantages of this invention will beapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a connection diagramschematically illustrating one embodiment of a capacitorpotentiometer'produced according to this invention;

FIGURE 2 is a connection diagram schematically illustrating one exampleof a rectifier circuit employed in this invention; and

3,478,256 Patented Nov. 11, 1969 FIGURES 3A and 3B are graphs forexplaining the operation of the circuit exemplified in FIGURE 2.-

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGURE 1 there is illustratedone example of a capacitor potentiometer of this invention, in whichreference character OS indicates a current-saturation type transistoroscillator comprising transistors Tr and TF3 and a transformer T, and Ea DC power source. The

- transformer T includes a primary winding 1 a secondary winding 1 andoutput windings 1 I and Reference character VR designates a voltagecontrol circuit consisting of transistor Tr and Tr,,, a Zener diode Dand a resistor R which controls an output voltage of the DC power sourceE. Reference character CV identifies a differential capacity changerincluding two variable capacitors C and C which are interlockinglydriven to vary their capacities in a differential manner. Referencecharacters RF RF and RF represent rectifier circuits each including asemiconductor diode, FL FL and FL smoothing circuits each consisting ofa resistor and a capacitor, R and R resistance voltage dividers, and Rand R resistance elements connected in series to each other andconnected in parallel to the variable capacitors C and C An outputterminal of the DC power source E is connected through the voltagecontrol circuit VR to a supply source terminal of the oscillator OS. Theoutput winding 1 of the transformer T of the oscillator OS has connectedthereto a series circuit of the differential capacity changer CVconsisting of the variable capacitors C and C and a series circuit ofthe resistors R and R The connecting point between the variablecapacitors C and C of the differential capacity changer CV and theconnecting point between the resistors R and R are connected across theinput terminals of the rectifier circuit RF Output terminals of therectifier circuit RF are connected across input terminals of theresistance voltage divider R through the smoothing circuit FL,consisting of a resistor r and a capacitor C The output winding 1 of thetransformer T is connected between the input terminals of the rectifiercircuit RF whose output terminals, in turn, are connected across inputterminals of the resistance voltage divider R through the smoothingcircuit FL consisting of a resistor r and a capacitor C An outputterminal of each of the resistance voltage dividers R and R is connectedin series to an output terminal labelled out in such a manner that anoutput voltage appearing at each voltage divider is added with that ofthe other. The output winding 1 of the transformer T is connected to theinput side of the rectifier circuit RF whose output side, in turn, isconnected across control signal input terminals of the voltage controlcircuit VR through the smoothing circuit FL consisting of r a resistor rand a capacitor C and the resistor R The oscillator circuit OS is causedto oscillate by an.

output voltage applied to its power supply terminal from the voltagecontrol circuit VR. The amplitude of the output voltage of theoscillator circuit OS is controlled within a certain range according tothe value of the voltage applied to the power supply terminal. Oneportion of an output signal of the oscillator OS is picked up by theoutput winding 1 of the transformer T, after which the picked-up signalis rectified by the rectifier circuit RF smoothed by the smoothingcircuit FL to be converted into a DC voltage in proportion to the valueof an AC output voltage of the oscillator circuit OS, thereafter beingimpressed to the control signal input terminal of the voltage controlcircuit VR. In the voltage control circuit VR the aforementioned DCvoltage is compared with a terminal voltage of the reference Zener diodeD by the transistor Tr by the output of which the transistor TF3 iscontrolled to adjust the output voltage of the voltage control circuitVR, thus controlling the output voltage of the oscillator circuit OS sothat the aforementioned DC voltage may be equal to the terminal voltageof the Zener diode D As a result of this, the amplitude of the AC outputvoltage of the oscillator circuit OS is always held at a certainvaluecorresponding to the standard voltage appearing across the terminals ofthe Zener diode D In the differential capacity changer CV the variablecapacitors C and C are formed symmetrical, which are ganged with eachother to be differentially driven. If now a displacement or rotationalangle of each capacitor is '0, the capacities-C and C of the capacitorsC and C respectively vary based on the following equations:

Where k is a constant and C0 is thecapacity of each of the capacitors Cand C when 0=O,'and the capacities of the capacitors C and C under thiscondition are set equal to each other.

The capacitors C and C of the differential capacity changer CV and theresistors R and R constitute a bridge circuit B, across the inputterminals of which the output voltage of the oscillator circuit OS isimpressed through the output winding of the transformer T.

If the impedance of the output winding 1 of the transformer T or theinternal impedance of the oscillator circuit OS is set small and-theload impedance of the bridge circuit B is set great, an AC voltage eappearing at the output terminal of the bridge circuit or impressed tothe inputterminals of the rectifier circuit RF is expressed by thefollowing equation:

is set equal to R1+R2 the AC voltage 6 is given by the followingequation:

As is apparent from the above equation, the output voltage c of thebridge circuit B is in proportion to the rotational angle 6 of thecapacitors C and C of the dilterential capacity changer CV. Further, theoutput Voltage 2 is independent of a factor such as a frequency andhence is not affected by the variations in the frequency of theoscillator circuit OS.

The output voltage 6 of the bridge circuit B produced in proportion tothe aforementioned rotational angle 0 is rectified by the rectifiercircuit RF and is smoothed by the smoothing circuit FL, to be convertedinto a DC voltage proportional to the output voltage e thereafter beingimpressed across the input terminals of the resistance voltage divider RWith a suitable setting of the voltage dividing value of the resistancevoltage divider R by adjusting its slider, the rate (span) of thevariations in the DC output voltage with respect to the rotational angleof the diflerential capacity changer CV can be set as desired.

The output voltage of the resistance voltage divider R is for adjustmentof thezero .point ofthe output voltage fed to the output terminal out,In thisembodiment the output of the output winding of the transformer Tis rectified by the rectifier circuit RF and is smoothed by thesmoothing circuit FL to obtain a certain DC'voltage. The resulting DCvoltage is divided at a desired value by the resistance voltage dividerF and is added to the output voltage of the resistance, voltage dividerR thus adjusting the zero point of the output voltage impressed to theoutput terminal labelled out."

When an AC voltage isr'e'ctified for obtaining a -DC voltageproportional to the ACvoltage,'if the'value'of the AC voltage is small,theoutput-DC voltage sometimes cannot be produced in proportion totheinput-AC' voltage due to the non-linear characteristic of thediodeincluded in the rectifier circuit. This defectcan be eliminated by" theprovision of such a compensating circuit as shown in FIGURE 2 in therectifier-smoothing circ'uit irr'FIG- A description. will be given inconnection with the compensating circuit andthe operation thereof; InFIG- URE 2 reference character RF designates a rectifier circuitconsisting of .diodes D to D FL a smoothing circuit consisting of aresistor R and a capacitor C, and CP. a compensating circuit consistingof a series circuit of diodes D and D and a resistor Rg'and connectedacross output terminals of the smoothing circuit FL.

The operation of the compensating circuit depicted in FIGURE 2 will bedescribed in connectionwith a case where an ACvoltage e, is impressedacross input termi-.

nals 1 and 2 of the rectifier circuit RF. In this case, a current flowsto the smoothing circuit FL in a certain direction through diodes D andD during every half cycle when the terminal 1 is made positive andthrough diodes D and D during every half cycle when the terminal 1 ismade negative, obtaining a rectified output across output terminals 3and 4. FIGURE 3A isa graphshowing a forward current-voltagecharacteristic of the diodes D to D of the rectifier circuit RFexemplified in FIGURE 2, the abscissa representing an impressed voltageV and the ordinate a current I. It appears from the graph of FIG- URE 3Athat .the voltage V and.the current I flowingthrough the diodes are innon-linear relation when the value of thetimpressed voltage V is small..FIGURE 3B is a graph showing the relations of the AC input voltage e, ofthe circuit depicted in FIGURE 2 to the DC output.

voltage E of the smoothing circuit FL andthe voltage E appearing acrossthe output terminals 3' and 4, the

abscissarepresenting the AC input voltage e tand the ordinate the DCoutputs E and E As is apparent from" from a curve a representing E 'echaracteristic, the

. relation between the AC input voltage and the DC output voltage Eproduced. by rectifying the. voltagefe varies in a non-linear mannerwhen the value of :the AC input voltage e, is small and the value'of theseries resistor R connected to the diodes is small. In order tocompensate forthis non-linear characteristic,- the. compensating circuitCP consisting of theseries circuit of the diodes D and D and theresistor R isinter-posed between the output terminals-of thesmoothingcircuit FL. The

diodes of the compensating circuit CP exhibit a non-linearcharacteristicsimilar to that of the diodes of the rectifier circuit RF, so that thenon-linearcharacteristic of -the rectified voltage produced by thediodesof the rectifier.

circuit RF, such as indicated by the curve'a, is'cancelled by thenon-linear characteristic of the diodes of the compensating circuit CP.As a result of this, the DC voltage E produced across the outputterminals 3 and 4 is proportionate to the AC input voltage e 'asindicated by a curve 11 in FIGURE 3B, even when the value of the ACinput voltage e, is small. Since the rectifier circuit RF is a full-waverectifier circuit and two diodes operate in forward direction duringevery half cycle, the two diodes are employed in the compensatingcircuit CF to compensate for the temperature characteristics of thediodes at the time of forward voltage drop of the diodes.

As will be clearly seen from the foregoing, the capacitor potentiometerof this invention employs a transistor osci lator of high frequency, andhence is small in power consumption and is almost free from adverseinfluences such as noise to ground and so on.

The present invention provides a non-contact type potentiometer ofrelatively small construction which is high-precision, highly reliableand long-lived.

It will be apparent that many modifications and variations may beeffected without departing from the novel concepts of this invention.

I claim as my invention:

1. A capacitor potentiometer comprising a DC power source; atransistor-fed DC-AC converter including a transistor and a transformerhaving a plurality of output windings, said transistor-fed DC-ACconverter converting ing the DC voltage of said DC power source into anAC voltage; a control circuit including a Zener diode and a controltransistor, said control circuit comparing output voltage obtained atone of said plurality of output windings of said DC-AC converter withthat across said Zener diode to control the voltage from said DC powersource by means of said control transistor to obtain a substantiallyconstant voltage from said -DC-AC converter; a bridge circuit consistingof a pair of series connected variable capacitors and a pair of seriesconnected resistors, said pair of resistors and capacitors connected inparallel, the junctions of said pair of resistors and capacitorsconnected across another one of said plurality of output windings ofsaid transformer of said DC-AC converter, means for difierentiallyvarying the capacitances of said pair of capacitors, and a firstrectifier circuit connected across the junction between said pair ofvariable capacitors and the junction point of said pair of resistors,whereby a DC output voltage can be obtained from said rectifier circuitwhich varies as a function of the means for varying the capacitances.

2. A capacitor potentiometer as claimed in claim 1, in which acompensating circuit is connected across the output of said rectifiercircuit, said compensating circuit composed of a resistor and a firstdiode connected in series.

3. A capacitor potentiometer as claimed in claim 2 comprising a seconddiode in said compensating circuit connected in series with the firstdiode and the resistor.

4. A capacitor potentiometer according to claim 1 comprising a secondrectifier circuit connected to a third output winding of saidtransformer, and the output of said second rectifier circuit connectedto the output of the first rectifier circuit to produce a compensatedoutput.

References Cited UNITED STATES PATENTS 2,274,735 3/ 1942 Peters et al340-200 2,548,790 4/ 1951 Higinbotham et al. 340-200 3,044,013 7/1962Peck 323- 79 X 3,121,839 2/1964 Malinick et a1. 323- 3,327,199 6/1967Gardner et al 321-2 3,350,623 10/1967 Clapp 321-8 JOHN F. COUCH, PrimaryExaminer W. H. BEHA, JR., Assistant Examiner U.S. Cl. X.R.

